FIG. 1 shows a structure of a touch panel including a visible area (VA) 1 and a black matrix (BM) area 2. The VA 1 includes a sensing unit made of indium tin oxide (ITO), a touch signal sensed by the sensing unit is transmitted to a flexible printed circuit (FPC) through traces in the black matrix 2, and further transmitted to an integrated circuit (IC) to be processed therein.
As shown in FIG. 2, a method for manufacturing the touch panel generally includes steps of: forming the sensing unit and the traces on a large glass substrate by an exposure process, a development process, and the like; cutting the large glass substrate to obtain a plurality of touch panels; and performing edge grinding, secondary screen printing and FPC bonding on each of the touch panels, so as to obtain a finished product. The secondary screen printing needs to be performed, because micro-cracks and notches will occur at an edge of each of the touch panels during the cutting and the edge grinding, damage the black matrix 2, and degrade the appearance of a product. Thus, a blank margin 3 having a width of about 0.5 mm will be introduced to each edge of the touch panels after the cutting and the edge grinding, and secondary screen printing is performed on the blank margin 3 of each edge of the touch panels after the edge grinding so as to print the blank margin 3 to be black.
FIG. 3 is a schematic diagram showing a screen printing device for secondary screen printing in the prior art, wherein, the peripheral blank area is a frame 41, mesh fabric 42 is provided inside the frame 41, the annular area in the mesh fabric 42 is an ink permeable area (also referred to as a “screen printing area”) 43, when a scraper 44 is driven to scrape the mesh fabric 42 in the direction as shown by the arrow in FIG. 3, ink permeates through the ink permeable area 43 but cannot permeate through a non-screen-printing area. That is, ink is filled into a stencil before performing screen printing, and then the scraper is driven to scrape the mesh fabric to enable the ink in the ink permeable area 43 to permeate through the ink permeable area 43, so that ink is printed onto the blank margin 3 on a surface of a touch panel.
Inventors of the present invention found that there exist at least the following technical problems in the prior art. On one hand, in the printing method of the above secondary screen printing, a large part of the portion, scraped by the scraper, of the mesh fabric does not belong to the ink permeable area. As a result, a large amount of ink remains on the large part of the mesh fabric, and less than 30% of the ink is printed onto the blank margin 3 on a surface of a touch panel. Thus, the large amount of ink is wasted, and the larger a size of the touch panel is, the lower a utilization ratio of the ink for screen printing is. On the other hand, in order to prevent the ink for secondary screen printing from contaminating the visible area 1 of a touch panel, a protection film for protecting the visible area 1 is generally attached to the touch panel to cover the visible area 1 before performing screen printing. Although the protection film is very thin, it results in a non-negligible segment difference (i.e., unevenness of a surface). The segment difference resulted from the protection film may cause the ink for screen printing in the ink permeable area 43 to have nonuniform thicknesses, wherein, the ink in an area close to the protection film has a large thickness, whereas the ink in an area far away from the protection film has a small thickness. In a severe case, “ink accumulation” and “ink overflow” may occur, and there is a risk that the scraper 44 may easily damage the mesh fabric 42.